LMK05028: Connecting a clipped sine wave to the TCXO input

Also, wanted to follow up that there doesn't seem to be a 0.6V offset on the TCXO input. Should I be able to measure that on the TCXO pin?

Hi Shivani,

Let me review your questions and reply shortly.

Regards,

Jennifer

Hi Shivani,

Can you please specify the slew rate of the TCXO input? The datasheet spec has a requirement for at least 0.2 V/ns, the higher the better.

Regards,

Jennifer

The new oscillator is the following

But we have some with the specs below as well

the second oscillator has too low a peak to peak output voltage so curious how to fix that as well

I have also discovered if I jump the signal from my board to the eval kit, it does offset the proper 0.6V

If the input buffer is powered down, does that remove the weak bias?

Looping in Kyle to help further support LMK05028 questions.

I'm trying to use the following TCXO that seems to have the correct slew rate and output voltage, however it has a very limited load requirement
https://www.txccorp.com/en/product-download/ak/
Why does the example provide such small resistors for the resistor divider? Wouldn't that draw a lot of current?

referring to the below section of the datasheet

Hello Shivani,

Are you able to get a closer capture of your TCXO input waveform so we can see what the actual slew rate is? Can you also on the same plot have markers to measure the Vpp swing.

Do you have a schematic for how your TCXO input is connected?

Also you sent plots for the TCXO input before and after 2 100nF capacitors. Which capacitors was this referring to? Is the design based on the EVM for the part?

Best Regards,
Kyle Yamabe

Hi Kyle,

Here are some more screenshots of the waveform

At the output of the oscillator

At the input of the PLL

I think the real issue is not the slew rate or amplitude but that there is no 0.6V offset from the PLL

Hi Shivani,

Can you please share your schematic of the LMK05028 for the custom board? If you are seeing the offset on the evaluation module then there could be something on your board that is causing the offset to not be present.

Regards,

Jennifer

Is this enough information?

Hi Shivani,

Thanks for sending the schematic. We are checking internally with design to understand more about the expected bias of the TCXO input and if that is the cause. The waveform you sent looks good to me--I'm not seeing anything glaringly wrong.

Regards,

Jennifer

Thanks Jennifer! Let me now if you need any additional information. Or if you are available for a call, perhaps that would help us resolve this more quickly